Warm Regime Research Articles

Early evidence of continental aridity and open-habitat grasslands in Europe as revealed by the Middle Miocene microflora of the Madrid Basin

In this study we present a new, extensive palaeobotanical and palaeoclimatic record from 85 microfloral assemblages of Middle Miocene (late Langhian–early Serravallian) age recovered from ten localities in the Madrid Basin. A large, shallow, slightly saline lacustrine system developed in the study area, promoting the occurrence of salt-tolerant plant communities on the lake margin. The regional landscape of the basin was characterised by grass-dominated, savannah-like vegetation under a warm (MAT: 13.8–18.8 °C) and semi-arid (MPwet: 151–71 mm, MPdry: 45–4 mm) climatic regime with marked seasonality of temperature and precipitation. These data re-open the debate on the origin of grasslands linked to dry conditions in Europe. Overall increased cooling and aridity through the Miocene led to the onset of grass-dominated habitats at the expense of forests, a process that in eastern Europe has been shown to occur from the Late Miocene. Our results, together with previous palaeobotanical and fossil mammal data from southern and central Spain, strongly indicate that open habitats were already prevalent in the Iberian Peninsula in the Middle Miocene, suggesting an earlier establishment here than in eastern Europe, possibly following a temporal pattern like the Anatolian Peninsula. The taxonomic diversity yielded by the samples from the Madrid Basin contributes to the understanding of the floristic composition of these early open habitats which were dominated by Poaceae, Amaranthaceae and Asteraceae with scattered shrubby and arboreal plants adapted to dry conditions such as Ricinus, Ephedra, Olea, Quercus, Acacia and Pinus. The age of the studied samples, coincident with the Middle Miocene Climatic Transition, indicates that this climatic episode marked an important step towards the establishment of open vegetation.

Thermionic emission of electrons from metal surfaces in the warm dense matter regime

Thermionic emission of electrons is a process fundamental to our understanding of laser–matter interactions in the ultra-short pulse regime. Charge collected from an emission process, as well the secondary radiation generated by their collective motion, provides avenues for diagnosing and verifying existing laser–solid interaction models. Laser fluences (∼104 J/m2) are of particular interest as they heat the surface electrons to temperatures on the order of a few electron volts (eV), placing it in the warm dense matter regime where much underlying physics is yet to be fully understood. However, even at such moderate fluences the conventional Richardson–Dushman formula for the emission rate becomes invalid. We consider an additional barrier potential on the surface that appears due to space-charge effects, which then limits the thermionic emission. This provides feedback leading to a self-consistent solution with the emission rate. Unlike the work function, this barrier dynamically evolves during the emission process. Here, we present the first calculation of the barrier potential on the surface, along with analytical expression, from a one-dimensional electrostatic model. The result is a generalization of the Richardson–Dushman picture to moderate laser fluences. The potential barrier has been incorporated into a two-temperature model for thermionic emission from an Al target irradiated by a femtosecond laser. The collisional and transport data for Al have been obtained using an average atom model.

Researching particulate matter characteristics for mitigating health risks generated by road vehicles

Research of PM (particulate matter) emissions is very important in crowded areas with high values of road traffic and industrial sites because may affect the health significantly. To mitigate the health risks generated by motor vehicles, the present paper shows the applied research on this topic with the practical results. The first important objective of the paper is to study the characteristics related to particulate matter in emissions generated by a car in actual road traffic test. The second objective is to compare the results from cold and warm operation regimes. It is important to know the trendline of PM emissions during operation due to their influence upon health. The PM amount is influenced by engine speed, fuel consumption and other operational factors. High levels of PM were recorded at 1500 rpm because it was the upper point in which the gear ratio has been changed.

Real-space Green's function approach for x-ray spectra at high temperature

There has been considerable interest in properties of condensed matter at finite temperature, including non-equilibrium behavior and extreme conditions up to the warm dense matter regime. Such behavior is encountered, e.g., in experimental time resolved x-ray absorption spectroscopy (XAS) in the presence of intense laser fields. In an effort to simulate such behavior, we present an approach for calculations of finite-temperature x-ray absorption spectra in arbitrary materials, using a generalization of the real-space Green's function formalism. The method is incorporated as an option in the core-level x-ray spectroscopy code FEFF10. To illustrate the approach, we present calculations for several materials together with comparisons to experiment and with other methods.

A meta‐analysis of the effects of global warming on rice and wheat yields in a rice–wheat rotation system

AbstractThe effects of global warming on crop production have received great attention in recent years. However, inconsistent results have been obtained with regard to major crops such as rice and wheat in rice–wheat rotation systems of China. Therefore, we undertook a comprehensive meta‐analysis of literature data. The yield response to warming differed for rice and wheat in the rice–wheat rotation system. Overall, warming significantly increased wheat yield (by 4.8%) but significantly reduced rice yield (by 14.8%). A number of factors were responsible for these observations. For example, rice yield responses varied with the temperature increase, variety and nitrogen (N) rate. Of these, N was the most important variable influencing yield responses to warming. The yield loss for rice was lower at temperature increases of 0.40–1.40°C and at a high N rate than that at temperature increases of 1.60–2.49°C and at a low N rate, respectively. The yield loss of indica rice was lower than that of japonica rice. For wheat, however, yield responses to warming varied with the warming regime, ambient temperature, temperature increases, and CO2 concentrations. Of these factors, ambient temperature was the most important variable influencing yield in response to warming. Warming increased wheat yield at a mean growth season temperature ≤10°C, temperature increases of 0.80–1.50°C, and at ambient CO2 concentrations. In addition, either daytime warming or nighttime warming significantly increased wheat yield. However, all‐day warming had no effect on wheat yields. We conclude that global warming will benefit wheat production but result in a serious loss of rice yield in rice–wheat rotations in China.

Bi-directional ferrite to austenite transformation through warm temperature deformation of a ferrite-based low density steel

The Gibbs energy model as an effective thermodynamic function along with detailed microstructural analyses were employed to assess the capability of strain induced transformations in a ferrite based lightweight steel. In this respect, the material was deformed in a warm temperature regime in compression mode and the resultant microstructures were studied in details. The progressive and extensive development of the banded structure was led to the partitioning of the ferrite phase and also the shearing of the parent austenite. The shear strain localization was effectively released through simultaneous transformation of ferrite to austenite and austenite to ferrite transformations as an effective strain compensation mechanism. This was led to appreciable flow softening in corresponding flow curves. The capability for bidirectional transformation resulted from the specified local elemental partitioning of Al and Mn and the resultant exactly same levels of Gibbs energies of each constituent phases.

Interplay of high-precision shock wave experiments with first-principles theory to explore molecular systems at extreme conditions: A perspective

Conventional methods for probing molecular changes in condensed matter systems, such as electronic and vibrational spectroscopy, are difficult to implement at the extreme conditions associated with dynamic compression experiments. This is particularly true for experiments in the multimegabar regime; to achieve the requisite energy density to produce such pressures, sample sizes are necessarily quite small and experimental timescales are, therefore, extremely short. Furthermore, these extreme pressure conditions also result in high temperatures and, therefore, significant thermal emission even in the visible to infrared regime and in some cases render the sample opaque or reflective, thereby precluding bulk spectroscopy techniques, such as Raman scattering. These experimental challenges require a different approach to evaluating shock-induced changes at the molecular or atomic level in the multimegabar or the so-called warm dense matter regime. The past few decades have seen significant advances in the use of first-principles methods to investigate materials under extreme conditions, enabling these methods to become a powerful tool for exploring molecular systems at extreme conditions. Here, we discuss the construct of combining high-precision shock wave experiments with first-principles theory to explore molecular systems at extreme conditions. The results from high-fidelity dynamic compression experiments are used to evaluate first-principles theoretical frameworks and identify the framework that best reproduces experimental results in the regime of interest. That validated framework is then used to perform detailed simulations of the system of interest, providing unique insight into the response of the system at the molecular level.

Plant developmental stage influences responses of Pinus strobiformis seedlings to experimental warming.

Seedling emergence, survival, morphological and physiological traits, and oxidative stress resistance of southwestern white pine (Pinus strobiformis Engelm.) were studied in response to warming treatments applied during embryogenesis, germination, and early seedling growth. Daytime air temperature surrounding cones in tree canopies was warmed by +2.1°C during embryo development. Resulting seeds and seedlings were assigned to three thermal regimes in growth chambers, with each regime separated by 4°C to encompass the wide range of temperatures observed over space and time across the species' range, plus the effect of heat waves coupled with a high carbon emissions scenario of climate warming. The embryo warming treatment reduced percent seedling emergence in all germination and growth environments and reduced mortality of seedlings grown in the warmest environment. Warm thermal regimes during early seedling growth increased subsequent seedling resistance to oxidative stress and transpirational water use. Experimental warming during seed development, germination, and seedling growth affected seedling emergence and survival. Oxidative stress resistance, morphology, and water relations were affected only by warming imposed during germination and seedling growth. This work explores potential outcomes of climate warming on multiple dimensions of seedling performance and uniquely illustrates that plant responses to heat vary with plant developmental stage in addition to the magnitude of temperature change.

Equations of state of poly- α -methylstyrene and polystyrene: First-principles calculations versus precision measurements

We show with a recently devised extended first-principles molecular dynamics method that calculated Hugoniots of poly-$\ensuremath{\alpha}$-methylstyrene agree well with precision experimental results of Kritcher et al. [Nature (London) 584, 51 (2020)] and D\oppner et al. [Phys. Rev. Lett. 121, 025001 (2018)]. The deviation is smaller than 0.8%. This agreement does not sensitively rely on the approximations in the employed first-principles methods as long as underlying physics are well described, as illustrated in the calculation of equation of state for polystyrene covering the warm dense regime. These results may stimulate a broad range of quantitative investigations on warm dense matter that were not thought possible before, and may thus afford a new prospect to the field of inertial confinement fusion and high-energy-density physics.

Impacts of climate change on terrestrial hydrological components and crop water use in the Chesapeake Bay watershed

This study assessed the impacts of climate change on terrestrial hydrological components and Crop Water Use (CWU) over the Chesapeake Bay watershed using a combination of Global Climate Models (GCMs) and a land surface model. To better understand the impacts of climate change on the hydrological cycle, long-term simulations of multiple earth system models from the Coupled Model Intercomparison Project (CMIP Phase 5) are statistically downscaled and bias-corrected using Multivariate Adaptive Constructed Analogs (MACA) scheme for use as model forcing. Precipitation indices from the twenty MACA-based GCMs are used to identify six best performing models. A mesoscale approach is developed, where CWU is estimated by accounting for the impacts of changing climate conditions and rising CO2 levels. Daily grid-based crop coefficients are derived from evapotranspiration data. The findings indicate a significant annual increase in precipitation (10 %) and temperature (+4.5 K) for the RCP 8.5 scenario towards the end of the 21st century. A significant reduction (13 % and 17 % respectively) in CWU is estimated for corn and soybeans, resulting from increased total precipitation and rising CO2 levels suppressing evapotranspiration. Our results indicate that even in a warmer regime, crop water use decreased due to rising CO2 concentrations due to climate change.

Growth and physiology of fourVitis viniferaL. cv. Tempranillo clones under future warming and water deficit regimes

Growth and physiology of four<i>Vitis vinifera</i>L. cv. Tempranillo clones under future warming and water deficit regimes

On the Hyperbolicity of the Bulk Air–Sea Heat Flux Functions: Insights into the Efficiency of Air–Sea Moisture Disequilibrium for Tropical Cyclone Intensification

AbstractSea-to-air heat fluxes are the energy source for tropical cyclone (TC) development and maintenance. In the bulk aerodynamic formulas, these fluxes are a function of surface wind speed U10 and air–sea temperature and moisture disequilibrium (ΔT and Δq, respectively). Although many studies have explained TC intensification through the mutual dependence between increasing U10 and increasing sea-to-air heat fluxes, recent studies have found that TC intensification can occur through deep convective vortex structures that obtain their local buoyancy from sea-to-air moisture fluxes, even under conditions of relatively low wind. Herein, a new perspective on the bulk aerodynamic formulas is introduced to evaluate the relative contribution of wind-driven (U10) and thermodynamically driven (ΔT and Δq) ocean heat uptake. Previously unnoticed salient properties of these formulas, reported here, are as follows: 1) these functions are hyperbolic and 2) increasing Δq is an efficient mechanism for enhancing the fluxes. This new perspective was used to investigate surface heat fluxes in six TCs during phases of steady-state intensity (SS), slow intensification (SI), and rapid intensification (RI). A capping of wind-driven heat uptake was found during periods of SS, SI, and RI. Compensation by larger values of Δq &gt; 5 g kg−1 at moderate values of U10 led to intense inner-core moisture fluxes of greater than 600 W m−2 during RI. Peak values in Δq preferentially occurred over oceanic regimes with higher sea surface temperature (SST) and upper-ocean heat content. Thus, increasing SST and Δq is a very effective way to increase surface heat fluxes—this can easily be achieved as a TC moves over deeper warm oceanic regimes.

Release of CO2 in Cold Subduction Zones by Hydrous Carbonatitic Liquids

AbstractThe release of CO2 from subducted slabs is an important process of the global carbon cycle. Previous studies have demonstrated that metamorphic reactions, carbonatitic melts, carbonate dissolutions, and hydrous carbonatitic liquids are effective CO2 recycling mechanisms in hot and warm thermal regimes, whereas the fate of subducted carbonates in cold subduction zones remains poorly understood. Here, we investigate the phase relations of subducted ophicarbonate at pressures beyond sub‐arc depths. The presence of complex quench textures indicates that hydrous carbonatitic liquids formed at temperatures as low as ∼850°C at depths of ∼300–440 km, which corresponds to cold thermal regimes. Water released by the decomposition of dense hydrous magnesium silicate phases can substantially affect the stability of subducted carbonates, which facilitates the formation of hydrous carbonatitic liquids. This provides a mechanism for scavenging CO2 from cold slabs and may promote the formation of metasomatized domains in the deep mantle.

Ocean acidification but not elevated spring warming threatens a European seas predator

Ocean acidification has the potential to negatively affect marine ecosystems by influencing the development and metabolism of key members of food webs. The garfish, Belone belone, is an ecologically important predator in European regional seas and it remains unknown how this species will be impacted by projected changes in climate. We artificially fertilized and reared garfish embryos until hatch at present (400 μatm) and future (1300 μatm) pCO2 levels within three temperature treatments, i.e. two daily warming regimes and one constant high temperature (17 °C). For the two warming treatments, embryos were fertilized at 13 °C and experienced 0.1 or 0.3 °C/day warming. The 0.1 °C/day treatment served as control: 13 °C was the in situ temperature of parental fish in the Southwest Baltic Sea and 0.1 °C/day is the average warming rate experienced by embryos of this population in nature. Survival was drastically reduced at both future pCO2 and at the constant high temperature while the highest survival in any treatment was observed at 0.3 °C/day warming. The proportion of embryos with morphological deformities increased with elevated pCO2 but not temperature. Hatch characteristics and physiological measures such as heart rate and critical thermal ranges, however, were not affected by pCO2 but were influenced by temperature. Our results suggest that garfish in the Baltic Sea will benefit from projected increased rates of spring warming but not the concomitant increase in pCO2. Previous studies on the impacts of ocean acidification on resident fishes in the Baltic Sea indicate that this piscivorous fish is at higher risk compared to its prey which may have broader implications for the future trophodynamic structure and function of the coastal food web.

Analytical representation of the local field correction of the uniform electron gas within the effective static approximation

The description of electronic exchange--correlation effects is of paramount importance for many applications in physics, chemistry, and beyond. In a recent Letter, Dornheim \textit{et al.} [\textit{Phys. Rev. Lett.}~\textbf{125}, 235001 (2020)] have presented the \emph{effective static approximation} (ESA) to the local field correction (LFC), which allows for the highly accurate estimation of electronic properties such as the interaction energy and the static structure factor. In the present work, we give an analytical parametrization of the LFC within ESA that is valid for any wave number, and available for the entire range of densities ($0.7\leq r_s \leq20$) and temperatures ($0\leq \theta\leq 4$) that are relevant for applications both in the ground state and in the warm dense matter regime. A short implementation in Python is provided, which can easily be incorporated into existing codes. In addition, we present an extensive analysis of the performance of ESA regarding the estimation of various quantities like the dynamic structure factor, static dielectric function, the electronically screened ion-potential, and also stopping power in electronic medium. In summary, we find that the ESA gives an excellent description of all these quantities in the warm dense matter regime, and only becomes inaccurate when the electrons start to form a strongly correlated electron liquid ($r_s\sim20$). Moreover, we note that the exact incorporation of exact asymptotic limits often leads to a superior accuracy compared to the neural-net representation of the static LFC [\textit{J.~Chem.~Phys.}~\textbf{151}, 194104 (2019)].

Changing River Network Synchrony Modulates Projected Increases in High Flows

AbstractProjections of change in high‐flow extremes with global warming vary widely among, and within, large midlatitude river basins. The spatial variability of these changes is attributable to multiple causes. One possible and little‐studied cause of changes in high‐flow extremes is a change in the synchrony of mainstem and tributary streamflow during high‐flow extremes at the mainstem‐tributary confluence. We examined reconstructed and simulated naturalized daily streamflow at confluences on the Columbia River in western North America, quantifying changes in synchrony in future streamflow projections and estimating the impact of these changes on high‐flow extremes. In the Columbia River basin, projected flow regimes across colder tributaries initially diverge with warming as they respond to climate change at different rates, leading to a general decrease in synchrony, and lower high‐flow extremes, relative to a scenario with no changes in synchrony. Where future warming is sufficiently large to cause most subbasins upstream from a confluence to transition toward a rain‐dominated, warm regime, the decreasing trend in synchrony reverses itself. At one confluence with a major tributary (the Willamette River), where the mainstem and tributary flow regimes are initially very different, warming increases synchrony and, therefore, high‐flow magnitudes. These results may be generalizable to the class of large rivers with large contributions to flood risk from the snow (i.e., cold) regime, but that also receive considerable discharge from tributaries that drain warmer basins.

Lattice stability of ordered Au-Cu alloys in the warm dense matter regime

In the warm dense regime, where the electron temperature is increased to the same order of the Fermi temperature, the dynamical stability of elemental metals depends on its electronic band structure as well as its crystal structure. It has been known that phonon hardening occurs due to an enhanced internal pressure caused by electron excitations as in close-packed simple metals, whereas phonon softening occurs at a specific point in the Brillouin zone as in body-centered cubic metals. Here, we investigate the dynamical stability of binary ordered alloys (Au and Cu) in the L1$_0$ and L1$_2$ structures. By performing first principles calculations on phonon dispersions, we demonstrate that warm dense Au-Cu systems show phonon hardening behavior except the lowest frequency phonon mode at point R of AuCu in the L1$_0$ structure. We show that when a phonon mode is stabilized by long-range interatomic interactions at ambient condition, such a phonon will be destabilized by the short-range nature of the warm dense matters.

Modeling of short-pulse laser-metal interactions in the warm dense matter regime using the two-temperature model.

A numerical model for laser-matter interactions in the warm dense matter regime is presented with broad applications, e.g., ablation, thermionic emission, and radiation. A unique approach is adopted, in which a complete set of collisional and transport data is calculated using a quantum model and incorporated into the classical two-temperature model for the electron and lattice-ion temperatures. The data set was produced by the average atom model that combines speed, conceptual simplicity, and straightforward numerical development. Such data are suitable for use in the warm dense matter regime, where most of the laser-matter interactions at moderate intensities occur, thus eliminating deficiencies of previous models, e.g., interpolation between solid and ideal plasma regimes. In contrast to other works, we use a more rigorous definition of solid and plasma states of the metal, based on the physical condition of the lattice, crystalline (ordered) versus melted (disordered), rather than a definition based on electron temperature. The synergy between the two-temperature and average atom models has been demonstrated on a problem involving heating and melting of the interior of Al by a short-pulse laser with duration 0.1-1 ps and laser fluences 1×10^{3}-3×10^{4}J/m^{2}(0.1-3J/cm^{2}). The melting line, which separates the solid and plasma regimes, has been tracked in time and space. The maximum melting depth has been determined as a function of laser fluence: l_{melt}(μm)≅4×10^{3}F(J/m^{2}).

Effects of ambient climate and three warming treatments on fruit production in an alpine, subarctic meadow community.

PremiseClimate change is having major impacts on alpine and arctic regions, and inter‐annual variations in temperature are likely to increase. How increased climate variability will impact plant reproduction is unclear.MethodsIn a 4‐year study on fruit production by an alpine plant community in northern Sweden, we applied three warming regimes: (1) a static level of warming with open‐top chambers (OTC), (2) press warming, a yearly stepwise increase in warming, and (3) pulse warming, a single‐year pulse event of higher warming. We analyzed the relationship between fruit production and monthly temperatures during the budding period, fruiting period, and whole fruit production period and the effect of winter and summer precipitation on fruit production.ResultsYear and treatment had a significant effect on total fruit production by evergreen shrubs, Cassiope tetragona, and Dryas octopetala, with large variations between treatments and years. Year, but not treatment, had a significant effect on deciduous shrubs and graminoids, both of which increased fruit production over the 4 years, while forbs were negatively affected by the press warming, but not by year. Fruit production was influenced by ambient temperature during the previous‐year budding period, current‐year fruiting period, and whole fruit production period. Minimum and average temperatures were more important than maximum temperature. In general, fruit production was negatively correlated with increased precipitation.ConclusionsThese results indicate that predicted increased climate variability and increased precipitation due to climate change may affect plant reproductive output and long‐term community dynamics in alpine meadow communities.

Extended carbon footprint and emission transfer of world regions: With both primary and intermediate inputs into account

By combining the latest statistics for the global economy in 2015, this study as a continuation of our previous work (Wu et al., 2020) investigates the extended carbon footprint of world regions and the emission transfer via commodity trade, by including both primary and intermediate inputs into consideration. The extended carbon footprint of the United States is revealed to be one and a half times as much as that of China, while this ratio is accounted as three quarters in our previous work, due to that final consumption takes a much larger share of the gross domestic product in the United States compared to the situation in China. CO2 emissions embodied in the primary inputs of the world economy are calculated to be equivalent to 42% of the emissions embodied in the genuine final consumption, highlighting the key role of capital goods in reallocating global carbon emissions. Moreover, emission transfer related with international commodity trade is explored, and the carbon trade links between major economies such as the United States, China, European Union, Russia, India and Japan are discussed in detail. In particular, the geographic and sectoral profiles for the carbon trade of the United States and China as two distinct economies are illustrated. It is revealed that Asia Pacific holds responsible for approximately half of the United States' carbon imports as well as China's carbon exports. Meanwhile, transport industry is taking up around one third of the United States' carbon exports while heavy and light industries totally dominate China's carbon exports. The outcome of this work may be supportive for providing more inclusive information regarding the establishment of global warming regimes, and may help us seek more informed policy choices and trade measures in global trade negotiations.